The present invention relates to communication systems. More particularly, and not by way of limitation, the invention is directed to a system and method for providing inbound roaming to an IMS-based network from 3GPP Home Networks that do not have an IMS infrastructure.
The IP Multimedia Subsystem (IMS), as defined by the Third Generation Partnership Project (3GPP), merges telephony and Internet technology by providing an all-IP based architecture for the telecommunications industry. The IMS is based on the Session Initiation Protocol (SIP) and makes heavy use of the protocols defined within the Internet Engineering Task Force (IETF). The system offers a network of servers and databases that assist a user agent with the task of establishing and managing sessions. IMS uses the term “sessions” because the connections between users are no longer limited to voice services (i.e., a phone call). Sessions may be voice, video, text, or other services connecting two or more user agents.
FIG. 1 is a simplified block diagram of the existing logical network architecture 10 for IMS. The IMS architecture includes a User Equipment (UE) 11, a Call Session Control Function (CSCF) 12, a Home Subscriber Server (HSS) 13, and Application Servers 14 and 15. The UE 11 is a device carried by a user that contains a SIP User Agent for initiating or terminating sessions. The CSCF 12 is responsible for managing the sessions including security and interconnection. There are three types of CSCFs. A Proxy CSCF (P-CSCF) sits at the edge of the network and is the entry point for the UE into the IMS core network. An Interrogating CSCF (I-CSCF) serves as the entry point into the network for peer networks. It also acts as a lookup function for finding the appropriate serving node for a subscriber. A Serving CSCF (S-CSCF) is responsible for authenticating the UE and managing ongoing sessions for the UE including invocation of applications. The S-CSCF communicates with the HSS 13 in order to retrieve the UE authentication information. After the user has been authenticated, the S-CSCF again communicates with the HSS, this time to retrieve the user profile, which specifies the services to which the user subscribes and which application servers are to be invoked for those services.
The HSS 13 stores the relevant user data including authentication information and service data. As part of the user profile, initial Filter Criteria (iFC) are defined to indicate which application servers are to be invoked based on information in the signaling plane. Application Servers 14 and 15 are invoked based on the iFCs that are stored in the user profile. The S-CSCF passes signaling to an Application Server if the criteria defined in the iFC are met. Once invoked, the application server participates in the session and provides additional capabilities.
FIGS. 2A-2B are portions of a call flow diagram illustrating the steps involved in an existing procedure for UE registration in an IMS network. 3GPP Technical Specification TS 23.228 requires the service control for Home-subscribed services for a roaming subscriber to be in the Home Network. In other words, the Serving CSCF must be located in the UE's Home Network. Thus, FIGS. 2A-2B illustrate UE 11 in Visited Network 21 registering with the Serving CSCF 22 in the Home Network 23.
Referring to FIG. 2A, the UE sends a SIP REGISTER message 24 to a Visited P-CSCF 25 to initiate the registration process. The Visited P-CSCF queries a Domain Name Server (DNS) 26 to locate a Home I-CSCF 27 in the Home Network 23 of the user based on the SIP Uniform Resource Identifier (URI) used by the UE. The Visited P-CSCF then forwards the REGISTER message to the Home I-CSCF. The Home I-CSCF 27 queries the HSS 13 to learn which Home S-CSCF 22 serves the user. The HSS responds with the information needed to determine the S-CSCF that will service this UE, and the Home I-CSCF forwards the REGISTER message to the appropriate S-CSCF 22.
The S-CSCF 22 queries the HSS 13 to retrieve the authentication information for the UE 11. The HSS responds with the authentication information, and the S-CSCF sends a 401 response message 28 back to the Home I-CSCF 27 to reject the REGISTER but includes authentication vectors so that the UE can authenticate. The 401 response message is returned to the UE via the Visited P-CSCF 25. The UE computes ciphering parameters based on the authentication information received in the 401 response message and establishes an IPSEC connection 29 with the Visited P-CSCF.
Referring to FIG. 2B, the UE 11 then uses the authentication information received in the 401 response message 28 to continue the registration process. The UE sends another SIP REGISTER message 31 to the Visited P-CSCF 25, and includes the authentication information. The Visited P-CSCF queries the DNS 26 to locate a Home I-CSCF 27 in the Home Network 23 of the user based on the SIP URI used by UE. The Visited P-CSCF sends the REGISTER message to the Home I-CSCF, which queries the HSS 13 to learn which Home S-CSCF 22 serves the user. The I-CSCF then forwards the REGISTER message to the S-CSCF. The S-CSCF verifies the authentication information from the UE and notifies the HSS that it will be servicing the UE.
The HSS 13 acknowledges the assignment and provides the S-CSCF 22 with the User Profile. The S-CSCF then sends a 200 OK response 32 back to the UE 11 via the Home I-CSCF 27 and the Visited P-CSCF 25. Based on initial Filter Criteria (iFC) for this user, the Home S-CSCF 22 may also initiate a 3rd Party Registration towards a Home Application Server 14/15 (FIG. 1). In this case, the Home Application Server responds with a 200 OK response back to the Home S-CSCF. After the UE 11 has registered with the Home Network 23, it can initiate a session. All session initiation traffic flows through the Visited P-CSCF 25, the Home S-CSCF 22 and, depending on session type, through the Home Application Server 14/15.
In 3GPP circuit-switched (CS) networks, the roaming user first attaches to the Visited Network where the Visited Network informs a Home HLR. Incoming calls to the user are handled utilizing a Mobile Station Roaming Number (MSRN) assigned by the Visited Network. The Home Network is not involved in outgoing calls.
FIG. 3 is a call flow diagram illustrating the steps involved in an existing Mobile Attach procedure in a 3GPP CS network. A 3GPP CS Mobile Station (MS) 41 sends a Mobility Management (MM) LOCATION UPDATE REQUEST 42 to a Visited MSC/VLR 43 in a Visited Network 44. The Visited MSC/VLR sends an UPDATE LOCATION message 45 to a Home HLR 46 in a Home Network 47 using the International Mobile Subscriber Identity (IMSI) provided by the MS. The Home HLR sends a Mobile Application Part (MAP) CANCEL LOCATION message 48 to a Home MSC/VLR 49. The Home MSC/VLR responds with a MAP CANCEL LOCATION ACK message 51, and the Home HLR sends a MAP INSERT SUBSCRIBER DATA message 52 to the Visited MSC/VLR 43, which contains the details of the subscriber profile and authentication vectors. The Visited MSC/VLR responds with A MAP INSERT SUBSCRIBER DATA ACK message 53, and the Home HLR sends a MAP UPDATE LOCATION ACK message 54 to the Visited MSC/VLR acknowledging the UPDATE LOCATION message 45. At this point the Home HLR knows the subscriber is roaming, or visiting, in the visited network.
The Visited MSC/VLR 43 then sends an MM AUTHENTICATION REQUEST message 55 to the MS 41 using authentication vectors received from the Home HLR 46. The MS responds with an MM AUTHENTICATION RESPONSE message 56, which includes a response to the authentication challenge sent by the Visited MSC/VLR. Using the outcome from the authentication process, the MS and MSC/VLR initiate ciphering over the air at 57. All messages are ciphered over the air from this point forward. The Visited MSC/VLR 43 then sends an MM LOCATION UPDATING ACCEPT message 58 to the MS in response to the MS's MM LOCATION UPDATE REQUEST 42. At this point, the MS is attached to the Visited Network 44.
FIG. 4 is a call flow diagram illustrating the steps involved in an existing procedure for a mobile terminating call in a 3GPP CS network. In this scenario, the Home MSC/VLR 49 receives a call from the Public Switched Telephone Network (PSTN) 61 through an ISDN User Part (ISUP) Initial Address Message (IAM) message 62, which is destined for the MS 41 roaming in the Visited Network 44. The Home MSC/VLR sends a MAP SEND ROUTING INFORMATION (SRI) message 63 to the Home HLR 46. The Home HLR in turn sends a MAP PROVIDE ROUTING NUMBER (PRN) message 64 to the Visited MSC/VLR 43. The Visited MSC/VLR responds with the MSRN at 65. The Home HLR 46 then responds to the Home MSC/VLR 49 with a MAP SRI message 66 containing the MSRN.
The Home MSC/VLR 49 uses the MSRN and forwards the ISUP IAM request 62 to the Visited MSC/VLR 43. The Visited MSC/VLR sends a CC SETUP message 67 to the MS 41. The MS responds by sending a CC CALL CONFIRMED message 68 to the Visited MSC/VLR. The MS then starts ringing and informs the Visited MSC/VLR with a CC ALERTING message 69. For simplicity, the Address Complete Message (ACM) has not been shown. The MS then sends a CC CONNECT message 71 to the Visited MSC/VLR when the call is answered. The Visited MSC/VLR then sends an ISUP Answer Message (ANM) 72 to the Home MSC/VLR 49. The Home MSC/VLR then forwards the ANM message to the PSTN 61. At this point, the call is established between the calling PSTN user and the called Mobile user.
As defined in 3GPP TS 23.228 (Version 7.12.0), the current solution enables inbound roaming to a pure VoIP IMS-based 3GPP-based network only from 3GPP Home Networks that have an IMS infrastructure. This is because the service control must always be located in the Home Network.